Hernandez was true to his word as he shut the Brewers down in order in the ninth to preserve a 2-1 win at Chase Field.
The win, combined with the Dodgers' 3-0 loss to the Rockies, increased Arizona's lead in the National League West to 2 1/2 games over Los Angeles.
Closing out games has been a problem for the D-backs, and after watching his bullpen meltdown in the series finale against the Dodgers on Wednesday, Gibson decided that whoever closes on a given night would be decided by matchups.
Brad Ziegler earned a save Thursday but had pitched in three straight games, so after using four relievers to get to the ninth, Gibson handed the ball to Hernandez, who entered the game with five blown saves, second-most in the NL.
Hernandez got Norichika Aoki to fly out before fanning Jean Segura and Carlos Gomez -- Milwaukee's two All-Stars -- to wrap things up.
"It's been frustrating for all of us," Hernandez said of the bullpen's struggles. "As bad as it's gone, we're in first place, so I feel like it really can't get any worse. Hopefully tonight was a start, and last night."
There were plenty of hold-your-breath moments for the D-backs in the innings leading up to the ninth as the Brewers stranded the bases loaded in the seventh and eighth innings.
"We don't do a good job with people on base," Brewers manager Ron Roenicke said. "To have that many opportunities and not to have somebody come through, it's just ... it shouldn't go on this long."
In the seventh, starter Patrick Corbin finally ran out of gas when he walked Segura to load the bases with two outs.
Gibson turned to reliever Will Harris, who got Gomez to strike out to end the inning.
J.J. Putz started the eighth and after he struck out Yuniesky Betancourt for the second out, Gibson brought in lefty Tony Sipp to face the left-handed-hitting Jordan Schafer, who Sipp walked to load the bases.
Once again Gibson made a change, this time bringing in Heath Bell to face pinch-hitter Martin Maldonado, and Maldonado hit a ball on the screws to center.
A.J. Pollock raced in, dove and at full extension was able to snare the ball to end the inning.
With all three runners on the move, had Pollock not been able to nab the ball, it could easily have turned into a 4-2 Milwaukee lead.
"I'm just glad I got a decent jump and a good enough of one to where I could lay out and get a glove on the ball," Pollock said. "That's the hardest part about the outfield, is having the confidence to know that you made the right decision to dive. In the outfield you've got to weigh the risk and rewards and see if it's the right opportunity. Tonight, obviously, you're selling out for that."
It was just the latest outstanding play in the outfield by Pollock this season.
"He has no regard for his body," Hernandez said. "He's willing to go into a wall, dive, slide, jump over somebody. It makes us want to be like him and I think other guys feed off that."
Defense would prove to be the difference in this game, which early on featured a classic pitchers' duel between left-handers Patrick Corbin and Tom Gorzelanny.
Corbin, who is headed to New York for next week's All-Star Game, allowed just one run over 6 2/3 innings while tying his career high with 10 strikeouts.
Gorzelanny, meanwhile, allowed a pair of runs on three hits in six innings.
While the Brewers made two crucial errors leading to both Arizona runs, the D-backs' defense made plays when needed.
"Sometimes you're not going to make a pitch and you're going to get saved by them more often than not," Hernandez said.
And that defense was one of the reasons the D-backs could be outhit 8-4 and go 0-for-6 with runners in scoring position yet still come out on top.
"It was one of those games where it could have gone either way," Pollock said. "And the good teams find a way to win those games, and we did enough to win the game."